As a structural element essential for a wireless communication, there is a local-oscillator signal generator circuit. Ordinarily, a voltage controlled oscillator is used for the local-oscillator signal generator circuit, and the oscillation frequency of the voltage controlled oscillator is controlled to determine the frequency range of the local-oscillator signal. Non-patent document 1: Takahiro Nakamura et al., “A fully Integrated 39.8-/43-GHz VCO-featuring Wide Tuning Range and Low Temperature-drift-for Single-chip MUX/DEMUX LSIs”, (U.S.A), Proceedings of 2004 IEEE Radio Frequency Integrated Symposium disclose an example of a voltage controlled oscillator that connects a changeable capacitor element to a resonation node of a differential oscillator with an LC resonator, and discretely changes over the oscillation frequency. Patent Document 1: Japanese Patent Laid-Open No. H8-204451 discloses an example of an oscillator and a filter which connect a negative capacitor that gives a negative capacitance between a resonant circuit including a piezoelectric oscillator and the ground, and is capable of adjusting the capacitance of a capacitor that is connected in parallel to the resonant circuit in a reducing direction thereof. In addition, Patent Document 2: Japanese Patent Laid-Open No. H10-256830 discloses an example of an oscillator circuit that uses a negative impedance circuit and changes an impedance of the negative impedance circuit according to a control voltage to change the oscillation frequency. Patent Document 3: Japanese Patent Laid-Open No. H10-247830 discloses an example of a negative amplifier circuit which applies a negative impedance circuit used in the above oscillator circuit to an amplifier.